A blog on consciousness by Janet Kwasniak

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Top-down control in action

The prefrontal cortex can select a rule to deploy in a particular situation. How is this done? The group of neurons that deploy a rule oscillate in synchrony when that rule is to be used. This synchrony explanation is becoming quite common. Synchrony is what produces functioning groups of neurons. Buschman at al have looked at rule selection in detail. However, I cannot access their paper. Fortunately two reviews of the paper are available (see citations).

Buschman used monkeys with electrodes implanted in their dorsolateral prefrontal cortex. They were taught to respond to the colour of a target and to the orientation of a target. They were presented with coloured targets that had an orientation. The decision for the monkey was which rule to use: colour or orientation discrimination. The monkeys were given a cue before the target that instructed them to use one rule or the other. In this way the researchers could see the events of choosing the rule.

The results –

The authors found that the local field potentials (LFPs) of a subset of the electrodes synchronized in the higher beta band (1940 Hz) around stimulus onset when the color rule was applied. When the orientation rule was applied, LFPs from a different set of electrodes synchronized in the same frequency band. Crucially, when the more difficult color rule was applied, the researchers observed pre-stimulus synchronization in the alpha band (616 Hz) for electrodes showing a preference for the orientation rule.

The oscillatory activity had consequences for behavior: especially stronger alpha-band synchronization allowed the monkeys to perform the task faster. In line with the behavioral effects, the higher the anticipatory alpha power for the orientation ensemble, the higher the spike rate of the color-rule ensemble during stimulus presentation. Additionally it was demonstrated that neuronal spiking was phase-locked to beta oscillations. … The strong phase- locking between spikes and LFPs demonstrates that the timing of neuronal action potentials is determined by the phase of ongoing oscillations. As such, oscillations are intimately involved in controlling the dynamics underlying neuronal computations. Oscillations might not only be important for creating neuronal ensembles within regions, but also for communication between distant regions.

This is interpreted to mean that the executive functioning in rule selection involves beta wave synchrony. This synchrony gathers together what is needed for the use of that rule in a discrimination. The alpha synchrony appears to suppress the default (orientation) rule so that the non-default rule (colour) is easier to deploy.

This seems to be what top-down control looks like.

For those of you that can access it, the Buschman paper is also listed below.